The present invention relates to a mold block which is used in a moving mold tunnel and which is particularly useful in the molding of profiled plastic pipe.
Corma Inc. of Toronto, Ontario, Canada has for many years been manufacturing and selling plastic pipe molding equipment. This equipment includes mold block sections circulating on endless tracks and meeting with one another to form complete mold blocks which are carried along a moving mold tunnel. The Corma mold blocks feature slit-like openings on the interior surfaces of the mold blocks which provide openings for drawing air out of the mold blocks. These vacuum slit bearing mold blocks have proved extremely efficient in the vacuum forming of plastic pipe where the vacuum has been induced from both mold block sections. They have also, to a lesser extent, been used in the blow molding of pipe.
To date, the Corma mold block has not been used for cooling purposes where it is very important to provide cooling of both the pipe and the mold blocks used in making the pipe. Such cooling substantially increases production speeds of the pipe mold.
It has now been discovered that by providing air flow controls at specified locations a mold block of the type described above can be used not only as it has been in the past, but for additional purposes as well.
More particularly, a mold block which is used with like mold blocks in a moving mold tunnel comprises first and second mold block sections, each of which has an air movement passage which includes an entrance, a first opening to the product shaping interior surface and a second opening to the parting face of each mold block section. When the two mold block sections are closed with one another at their parting faces, the parting face opening in the first mold block section meets with the parting face opening in the second mold block section.
Also provided are first and second air flow controllers which are movable independently of one another between an air flow and an air blocking position. The first air flow controller is located between the parting face opening and the interior surface opening in the passage in the first mold block section and the second air flow controller is located between the entrance and the interior surface opening in the passage in the second mold block section.
A mold block as described above can be used in any one of four different modes of operation including a first vacuum forming mode in which air is withdrawn from the mold block through both mold block sections, a second vacuum forming mode of operation in which air is withdrawn from the mold block through only one of the mold block sections, a third cooling mode of operation in which air is introduced to the mold block through one mold block section and is withdrawn from the mold block through the other mold block section, and a fourth blow molding mode in which air pressure is released from the mold block through both mold block sections.
In accordance with the present invention, a mold block having air flow controllers as described immediately above, has substantially enhanced versatility over the known Corma mold block.